Add support for nicer environment variable definition

```
# Env vars
scw container container update f61a11c0-bc04-4029-8c1a-c207cdfb75e1 environment-variables."MYKEY"="MYSECRET"

# Secret env vars
scw container container update f61a11c0-bc04-4029-8c1a-c207cdfb75e1 secret-environment-variables.0.value="MYSECRET" secret-environment-variables.0.key="MYKEY"
```

It would be useful to have something more consistant between those 2 calls.